Ryukin, Carassius auratus auratus
Swim bladder disorder is very common in poorly bred fancy goldfish, it occurs when the fish's swim bladder doesn't develop or work properly. Some fish are born with a defect and this is untreatable. It causes the fish either to float like a cork or sink like a stone and in the worst cases this is combined with the fish unable to keep its equilibrium. In such cases the only sensible option is euthanasia or the fish will have to suffer a pretty miserable existence and a prolonged death.
Some fish lack a swim bladder, instead they rely on dynamic lift from angling their pectoral fins to generate lift as they move forward. But most fish have a swim bladder, apart from some bottom living fish and all cartilaginous fish such as sharks and rays, where it is reduced or even absent because it is less important to them and could even be a hindrance.
The most common method of controlling buoyancy for fish is by gas filled swim bladders. The gas in the bladder is obtained from the fishes blood through a vascular rete known as the gas gland, or by gulping air from the surface in fishes which have a link from the gut to the swim badder. So the fish can increase or decrease the gas in the bladder in order to increase or decrease buoyancy in order to maintain neutral buoyancy..
The swim bladder is so sensitive that fish can detect changes in depth measuring just 0.1% of the depth that the fish is at. Also if the surrounding water pressure is decreased by a factor of three i.e. if a fish is brought to the surface from great depth then the swim bladder will rupture. This is important to know because many people still take fish home in a plastic bag which is then floated in their aquarium for a while before the fish is released. Quite often the bag is punctured by pushing a thumb through the bag until it pops and then the bag is tore open and the fish released. But pushing a thumb through the bag cause a sudden rise in pressure in the bag and then an explosive decompression when the bag is punctured. This process could easily cause permanent damage to the swim bladder and so should be avoided, cut the bag open instead as a safe alternative.
In some cases when the swim bladder is connected to the fishes vascular system the organ can be used as a rudimentary lung which allows the fish to live in water with a low oxygen level where it would normally fail to survive.
There are different types of problems which can occur to swim bladders. A fish may have a malformed swim bladder, this is often the case with fancy goldfish where their body shape has been altered through selective breeding to make it shorter and deeper. This means that the fishes internal organs are not where they should be. The position and size of the swim bladder is of paramount importance and any alteration is likely to cause problems. With fancy goldfish the potential problems can be minimised by keeping them in fairly shallow water and by paying particular attention to their diet and feeding regime. A high fibre diet with the fish being fed little and often is the ideal and avid feeding the fish with to much dried flake and most importantly avoid feeding at the surface.
Quite often a digestive problem of trapped gas in the fishes gut either from poor diet or gulping air as the fish eats. This trapped gas obviously creates extra buoyancy which the fish cannot control and this is a digestive problem and nothing to do with the swim bladder although it is often put down to this.
The 'cure' for this is to switch to a better diet, often peas are mentioned or recommended. This will of course work but although fresh greens will cure the digestive problem they will have no bearing on a real swim bladder problem.
If the swim bladder is malformed, displaced or has been permanently damaged then there is no cure or treatment.
Anything which interferes with the gas exchange within the swim bladder will potentially result in the bladder not functioning properly. A number of diseases could possibly lead to swim bladder disorder:
Aeromonoas hydrophila (bacterial) infection leads to thickening of the bladder walls and filling the bladder with fluid.
Trematodes and nematodes can infect the bladder causing imflamation.
If the cause is correctly diagnosed then the appropriate treatment can be given, but don't assume anything, using the wrong medication won't help and may even make things worse.
The swim bladder is a delicate organ and is easily damaged through poor handling. If trauma is known to be the cause of the disorder then try keeping the fish in a separate tank with just enough water to cover the fish, aerate the water well and raise the temp by just a few degrees and don't feed the fish while under treatment. Keep the fish like this with as little disturbance as possible for 5 - 7 days, this will allow the bladder time to heal through being rested.;
Wikipedia - swim bladder
Biology of fishes by Q Bone, N. B. Marshall and J H S Blaxter.
Aquariology Master volume by Dr John B Gratzek